RE: Lost Plane alarms
Yes there are several different designs available. Just a word of advice, use one that has it's own integral power supply. Do not count on the receiver battery to do the job as, in many crashes, the battery becomes disconnected from the receiver. Most are just a pulse emmission detector (usually an LM555 and associated circuitry) with a 9 volts dry cell and switch opperating a solid state audio device.